Color Diversity And Its Adaptation Of The Stigma In Angiosperms

The flower is the reproductive organ of angiosperms.An exploration of floral color diversity is helpful for us to understand the evolution of angiosperms,Color diversity can occur in different species,but also in the same species,in different structures or tissues,even at different positions of the same structure/organ.Compared to the corolla,the color diversity and its adaptation of stigma are rarely concerned,and a comparative study of the stigma color based on modern phylogeny remains unknown.To understand the adaptive strategies of the stigma color of flowering plants in natural communities,we measured the surface color of 117 species(34 families and 82 genera)in the Shangri-La Plateau Ecological Education Ministry Field Station in Yunnan Province,including stigma,style,pollen,anthers and corolla in July-September 2020.Flower colors were measured in March,April,and June 2019 respectively in three natural communities,in Jincheng Mountain Forest Park(23 species)in Sichuan Province,Tangjiahe National Nature Reserve(21 species)in Sichuan Province,and Tiantangzhai Scenic Area(16 species)in Hubei Province.For the color of the plant stigma,we propose that the stigma color has protective effect on the pollen,and the bees cannot accurately distinguish the pollen falling on the stigma so that reduce the collection of pollen.117 species were categorized into two groups based on whether the stigma is covered by corolla:the stigma exposed group and stigma hidden group.Our results showed that the stigma color in the studied species is diverse,from white to purple,mainly yellow and white.Under the vision of bees,the same color is not exactly the same effect on the insects.Among stigma exposed species,the stigma color is more diverse.Our measurement of color contrast between the stigma and style showed that 57 species(52.14%)shared the same but 60 species(47.86%)differed;the stigma color was similar to pollen color in 74 species(63.25%),but not in 43 species(36.75%);the stigma shared anther color in 71 species(60.68%),but not in 46 species(39.32%);the stigma shared corolla color in 57 species(48.72%),but not in 60 species(51.28%).Compared the color distance between the stigma and style,pollen,anther and corolla,we found that the stigma color is closest to the style,followed by pollen color,which showed that for visiting insects,especially bees,it is not easy to distinguish the color of the stigma from the pollen,and supports the view of its color hiding and protecting the pollen.Small color distance between the stigma and style suggests that the color variation of the same structure will also be affected by phylogeny.This comparative survey of stigma color is the first empirical study of the color diversity to explore the potential reproductive strategies in natural communities,we observed color differentiation in different floral organs.The color contrast between the stigma and pollen is little in most species which might help hide pollen,but we still need further experiments to test this finding.